Sometimes you get an assignment that allows you to choose the topic or where to focus within a certain subject. While these assignments allow you to customize your learning, it can also be frustrating to decide what to focus on.
Start by looking at the expectations of the assignment and discussing any questions with your instructor. Your instructor may also be able to make suggestions of topics to write about.
Then consider what excites you about the topic or what you would like to learn more about. Sometimes doing a library search will give you ideas of what topics are possible within that broader subject. Look around until you find something that makes you feel interested or fits your bigger goal for your degree.